A ferrite scanning line source is a linear ferrite loaded waveguide having a series of radiating apertures regularly spaced along the length of the waveguide. These line sources, in the past, have been formed from cylindrical columns of solid phase shifting ferrite material having a conductive sheath and a series of radiating apertures. Planar array antennas were formed by arranging several of these columns of scanning line sources in an array to form the antenna.
Conventional phase scanning antennas generally required thousands of radiating elements with associated connectors, power dividers, phase shifters, phase shifter drivers and transmission lines. Due to the smallness of antennas of the high microwave and millimeter wave frequencies, the radiating elements and other associated components are small and difficult to fabricate. For this reason, a ferrite scanning line source greatly simplifies a phased array antenna. An example of a conventional ferrite scanning line source is disclosed in U.S. Pat. No. 4,613,869, entitled "Electronically Scanned Array Antenna". Conventional ferrite scanning line sources have been large, inefficient or the coupling valves have been unstable with magnetization. Accordingly, there has been a long-felt need for a more compact and efficient ferrite scanning line source in which the RF H field at the coupling slots has minimum variation with phase state, and therefore minimum coupling value variation with scan angle.
Small high performance phase shifters have been recently developed for use in antennas operating in the microwave and millimeter wave frequency range. Examples of these phase shifters, known as hybrid mode phase shifters, are disclosed in commonly-assigned U.S. Pat. Nos. 5,075,648 and 5,170,138, both of which are incorporated by reference. Hybrid mode phase shifters have principally been applied as components to individual antenna radiator elements for phased array antennas. Individual radiator elements each having a hybrid mode phase shifter and an electronic driver are more complex and expensive than a ferrite scanning line source. Prior to the present invention, it was unknown how to minimize the RF H field variation at the coupling slots with variation in the scan angle when utilizing the transverse magnetized toroidal phase shifter (i.e., hybrid mode phasers) for ferrite scanning line sources. In addition, prior to the current invention, it was unknown how to solve the multiple reflection problems associated with radiating aperture and coupling slot impedance mismatches.